Alexander entered India in 327, encountering some of the toughest fighting of his career in the the crossing. He reached the Indus River in 326.
None of the Greeks had ever encountered anything to prepare them for India. The terrain, the monsoons, the fierce tribes, all combined with the long years of campaigning to take some of the heart out of the Macedonians.
Alexander's geographers had assured him that just beyond India was Ocean, the great body of water that completely encircled the world. India itself was surely no bigger than the Persian Empire. We do not know what what in Alexander's mind, but most historians guess that he had no idea of the true size of the subcontinent and that he truly believed he need make only one more push to bring all the eastern world under his dominion.
Defeat of Porus
Two factors combined to bring Alexander's march to a halt: he began to realize that India was much bigger than he had thought, and a war with an Indian king named Porus showed that India would not fall easily to the Greeks.
Porus was powerful both as a man and a king. He stood seven feet tall, a widely-feared ruler and warrior. He fielded an army that was a match for the Greeks, but Porus' army had an additional advantage: war elephants.
This marked their first real encounter with elephants in battle, and it terrified the Greeks. Worse yet, Alexander met Porus during the monsoon season and faced him across a river in flood.
Despite all this, Alexander defeated Porus, killing the king's two sons. Alexander forced Porus into an alliance, a policy he had followed elsewhere.
Mutiny
Having secured the upper Indus River valley, Alexander began to push into the interior of India. The land became dry, but the cities and kingdoms were formidable. As they pressed on, the locals spoke of endless kingdoms to the east, and another great river, and still more kingdoms beyond that. No one knew of any end to them.
At last, his men refuse to go any further. They had refused before, more than once. Each time, Alexander harangued and persuaded and sulked in his tent for days, and eventually the men, terrified of the prospect of being without their hero, had given in.
Not this time. Alexander realized the temper of his army and reluctantly gave the command to return to Persia. This was no small task in itself. Going back by way of the Himalayas and Afghanistan was out of the question. The best course seemed to be to work their way down the Indus River to the Indian Ocean.
The Return
It took a year to do it. The Greeks had to fight their way down the Indus, the lower course of which had many strong cities. At one of these, Alexander was wounded by an arrow that pierced his lung. For three weeks he was near death, but he eventually recovered.
Once at the Indian Ocean, the Greeks built a fleet of ships. Half the army travelled with Nearchus by sea, while Alexander took the other half by land along the coast, each army supporting the other. The return to Persian was a heroic accomplishment and is yet another testament to the strength of discipline among the Macedonians.
Alexander reached Susa in 324. He had been on campaign continuously for five years.
